High altitude pressure responsive capsule



Sept. 22, 1953 D. F. MURPHY 2,652,859

HIGH ALTITUDE PRESSURE RESPONSIVE CAPSULE Filed May 18, 1948 I RY 10 )6 o PRESSURE DOnaldIMurphy At to rlzey Patented Sept. 22,

UNITED STATE HIGH ALTITUDE PRESSURE RESPONSIVE CAPSULE Donald Francis Murphy, Baltimore, Md., assignor to Bendix Aviation Corporation, Baltimore, Md.,

a. corporation of Delaware Application May 18, 1948, Serial No. 27,755

3 Claims. 1

This invention relates to devices for converting pressure variations into mechanical displacements and more particularly to a device of this nature having arelatively large deflection-pressure modulus in the presence of low pressures and a relatively small deflection-pressure modulus in the presence of pressures exceeding a predeter mined. level.

In making precise pressure controlled measurements at relatively low pressures, it is desired that the mechanical pressure sensing unit be characterized by a large displacement for a small pressure change. The satisfaction of this requirement with a unit having a constant deflection-pressure modulus results in an assembly having an excessive travel which may be diflicult to accommodate in an indicating unitintended to provide accurate indications'in a limited low pressure range. It has previously been the practice to employ stops disengaging the lever arm or other transmission link from the pressure driving unit whenever its deflections fell without a predetermined range. Such stops, however, being separate from the pressure responsive driving unit and usually associated witha lever system burdened by variable and unpredictable amounts of play, have not proven entirely satisfactory. Further, it is fundamental in instrumentation that an increase in the number of elements participating in a given observation must inevitably vitiate the over-all accuracy to be obtained. Such an arrangement further distributes 2 capsule assembly embodying the principles of the invention and Figure 2 illustrates graphically the deflectionpressure characteristic of the improved pressure capsule.

The capsule assembly includes a base disk I I having an apertured boss I] located centrally thereof. The bellows side of the base disk II is also provided with a central elevated land 20 which is circular in form. In. addition, the mounting disk II is apertured at the point I0, radially displaced outwardly of the land 20, to receive an exhaust'tubulation I8. If the mounting disk I I is of brass or some other material to which solder adheres readily, the exhaust tubulation I8 may be hermetically sweated in place.

An inner Sylphon bellows I6 of substantially cylindrical form has its open end sweated to the mounting disk II along the periphery of the circular land 20. The inner bellows I6 may be formed of a single sheet of material and have a closed end which is a continuation of that matecritical elements at spaced points in the instrument structure, rendering it sensitive to mechanical distortions arising from thermal changes and rough handling.

Accordingly, it is an object of the present invention to provide a new and novel pressure responsive mechanical driving unit intrinsically possessing a relatively large deflection-pressure modulus in the presence of low pressures and having means therein to preventv deflection in the presence of pressures exceeding a predetermined level.

It is an'other object of the invention to provide a new and novel pressure capsule assembly having a high deflection modulus in low pressure regions and having means to prevent deflection v for pressures exceeding a selected value.

Still another object of the invention is to provide a new and novel pressurecapsule assemblyin which the threshold of pressure indication may be conveniently adjusted.

Other objects and advantages of the invention will in part be obvious and in part be described when the following specification is read in conjunction with the drawings in which rial. The aperture of boss Il may be tapped and a threaded rod I3 with an enlarged end inserted therein with the enlarged end adjacent the end of the inner bellows I6 remote from the mounting disk I I: A collar I4 is slipped over the shank I3 and sweated into I of the threaded member place at the closed end of the inner bellows I6 in a position retaining the enlarged head of the threaded adjusting member I3 in engagement with a spring washer I9. It may be noted from I If more convenient, the order of assembly may be Figure 1 is a sectionalview through a pressure reversed. The driving disk I2 is similarly provided with an apertured boss whose aperture does not, however, extend through the driving member I2. This aperture may be tapped to receive a suitably threaded screw for easy connection with a driving link conveying the capsule motion to an indicator assembly. The inner Sylphon bellows I6, mounting disk II, outer Sylphon bellows I5, and the driving disk I2 define a sealed chamber venting to the exhaust tubulation I8. Thishermetically enclosed volume may be exhausted to any desired pressure by connecting the tubulation I8 with an evacuating system and sealing ofi the tubulation when the desired residual pressure within the sealed volume has been secured. The outer bellows I5 is relatively soft and is characterized by a large deflection-pressure modulus,

bellows l and the table formed thereby. A

partial withdrawal of the adjustment screw l3 permits the beginning of deflection at a relatively high pressure while its advancement, with consequent similar displacement of the limiting table formed by the inner bellows l6, decreases the pressure at which displacement beings in the presence of diminishing ambient pressure.

At the relatively high pressure corresponding to ground level, the flexible outer bellows i5 is driven toward the mounting disk H to firmly engage the driving disk l2 with the limiting table formed by the inner bellows I6. As the pressure is decreased, the force maintaining these two members in engagement decreases correspondingly until the pressure force equals the distortion-induced restoring force built up within the outer bellows l5. A-continuing reduction in pressure permits the bellows spring force to move the driving disk I2 outwardly away from the limiting table formed by inner bellows I 6.

The displacement characteristic of the composite pressure capsule assembly is graphically illustrated in Figure 2 in which increasing pressures are indicated by increasing displacements to the right on the abscissa and increasing displacements are indicated by increasing distances along the ordinate axis. When the pressure exceeds the critical value at 22, the driving disk and limiting table or abutment are in engagement and there is no travel of the driving disk as is at once evident from an inspection of the figure. A decrease in the pressure below the value corresponding to point 22 permits the bellows spring force to overcome the pressure-induced force with consequent increase in displacement along the line 23 until a travel corresponding to the point 2| has been attained at zero pressure.

The composite assembly just described is a compact pressure responsive driving unit satisfying the requirements developed earlier in this specification. It may be beneficially employed wherever a high deflection rate over a limited range of low pressures is required without the possibility of imparting excessive motions to sensitive lever systems in the presence of very high pressures.

There will be obvious to those skilled in the art many minor variations and modifications not departing materially from the principles of the invention, as they are capable of wide application.

What is claimed and desired to be secured by United States Letters Patent is:

1. A pressure responsive device having a substantially large deflection-pressure modulus in the presence of pressures not exceeding a predetermined pressure level and having means to prevent defiection in the presence of pressures greater than said predetermined level, comprising, in combination, a first flexible sealing partition having a substantially cylindrical form with one closed and one open end, a second flexible sealing partition having a smaller substantially cylindrical form with one closed and one open end situated within said first partition with its closed end adjacent the closed end of said first partition, a base member hermetically engaging said open ends and having an aperture within the region bounded by said second partition, and a member passing through said aperture adapted to maintain the closed end of said second partition at a desired distance from said base member, the volume between said partitions being evacuated to a residual pressure of very nearly zero absolute pressure.

2. A pressure responsive device having a substantially large deflection-pressure modulus in the presence of pressures not exceeding a. predetermined pressure level and having means to prevent deflection in the presence of pressures greater than said predetermined level, comprising, in combination, a first flexible sealing partition having a substantially cylindrical form with one closed and one open end, a second flexible sealing partition having a smaller substantially cylindrical form with one closed and one open end coaxially situated within said first partition with said closed ends adjacent, a base member hermetically engaging said open ends and having a threaded aperture coaxially situated with respect to said cylindrical partitions and a correspondingly threaded member extending through said aperture to a point adjacent the closed end of said second partition, the volume between said partitions being evacuated to a residual pressure of very nearly zero absolute pressure.

3. A pressure responsive device having a substantially large deflection-pressure modulus in the presence of pressures not exceeding a predetermined pressure level and having means to prevent deflection in the presence of pressures greater than said predetermined level, comprising, in combination, a first flexible sealing partition having a substantially cylindrical form, a disk sealingly engaging one end of said first partition, a second flexible sealing partition having a small er substantially cylindrical form with one closed and one open end coaxially situated within said first partition with said closed end adjacent said sealing disk, 2. base member hermetically engaging the other end of said first partition and said open end of said second partition and having a threaded aperture coaxially situated with respect to said cylindrical partitions, a correspondingly threaded member extending through said aperture and having an enlarged portion adjacent the closed end of said second partition, and a collar secured to said closed end of said second partition embracing said enlarged end of said threaded member, the volume between said partitions being evacuated to a residual pressure of very nearly zero absolute pressure.

DONALD FRANCIS MU RPHY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,345,547 Roth Mar. 28, 1944 2,454,423 Baak Nov. 23, 1948 FOREIGN PATENTS Number Country Date 611,546 Great Britain of 1948 698,427 Germany Nov. 9, 1940 

